1. Field of the Invention
The present invention relates to a method of measuring a total amount of latent image charge, an apparatus measuring a total amount of latent image charge, an image forming method using a result by the measurement method or the measurement apparatus, and an image forming apparatus, such as a copier, a printer, a facsimile, a plotter and an MFP that includes at least one of these, using a result by the measurement method or the measurement apparatus.
2. Description of the Related Art
Controlling a toner attachment amount is important for an electrophotography process. For this purpose, an amount of latent image charge that disappears by exposure is preferred to be appropriately controlled. However, fatigue of a photosensitive element in association with environmental change and continuous operation changes a total amount of latent image charge even if exposure energy and a charge potential is not changed. In view of this, it is preferred to precisely acquire a total amount of latent image charge of an electrostatic latent image, which is formed under a process condition, characteristics of the photosensitive element, and an exposure condition.
In a parallel plate capacitor model, in the case where a potential difference V is applied across electrode plates of a capacitor with electric capacitance C, an electric charge Q stored in the capacitor is proportionate to V and the following relation is satisfied:Q=CV Under this condition, the amount of electric charge is proportionate to the electric potential. Accordingly, simply obtaining the electric potential allows easily measuring the charge amount. Because a target latent image charge of the present invention is a small charge such as from several micron to hundreds micron, the relation of Q=CV in the parallel plate capacitor model is not satisfied. In view of this, conventional method has not allowed accurately measuring the amount.
As a method of observing an electrostatic latent image using an electron beam, a method disclosed in Japanese Patent Application Laid-open No. H3-049143 has been known. However, the sample is limited to an LSI chip and a sample that can store and hold the electrostatic latent image. That is, measurement is impossible in a general photosensitive element where dark decay occurs. A general dielectric semipermanently holds an electric charge. Thus, an amount of electric charge can be measured using a large amount of time after a charge distribution is formed without any influence on a measurement result. However, since the photosensitive element does not have an infinite resistance, it cannot hold the electric charge for a long period of time, causing dark decay and thus decreasing a surface potential with time. The photosensitive element can hold the electric charge for several tens of seconds at most even in a darkroom. Therefore, when attempting to observe the electrostatic latent image through a scanning electron microscope (SEM) after charging and exposing, the electrostatic latent image will disappear during the preparation stage.
In view of the above-described circumstances, the applicant has proposed a method that allows measuring an electrostatic latent image even using a photoreceptor sample with dark decay (see Japanese Patent Application Laid-open No. 2003-295696 and Japanese Patent Application Laid-open No. 2004-251800). A charge distribution on a sample surface forms an electric field distribution in a space corresponding to the surface charge distribution. In view of this, in the case where the sample surface is scanned with a charged particle beam, a secondary electron generated by that an incident electron reaches the sample is pulled back by this electric field. This reduces the amount of the secondary electrons that reach the detector. Therefore, this provides a contrast where a portion with an intense electric field becomes dark and a portion with a weak electric field becomes bright, thus allowing detection of a contrast image corresponding to the surface charge distribution. Accordingly, when exposure is performed, an exposed portion appears black and a non-exposed portion appears white. Thus, the formed electrostatic latent image can be measured. Additionally, this applicant has proposed a method where measurement is performed under a condition that there is a region where a velocity vector of an incident charged particle perpendicular to a sample is reversed (see Japanese Patent Application Laid-open No. 2005-166542). Use of this method allows visualizing a latent image profile in the order of micron, which was conventionally difficult.
As described above, accurately measuring the total amount of the latent image charge that disappears by exposure allows controlling the toner attachment amount with high accuracy, thus contributing to high image quality. However, the method disclosed in Japanese Patent Application Laid-open No. 2005-166542 can visualize the electrostatic latent image, but cannot accurately measure the total amount of the latent image charge.
In view of the above-described circumstances, there is a need to provide a method of measuring a total amount of latent image charge that allows accurately measuring a total amount of latent image charge and contributing high image quality by reflecting a result of the measurement on the control of the toner attachment amount.